This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. Therefore, unless otherwise indicated herein, what is described in this section should not be interpreted to be prior art by its mere inclusion in this section.
The international patent application PCT/SE2013/050336 which was filed on Mar. 26, 2013 by Telefonaktiebolaget LM Ericsson (publ.), proposes a method performed by a radio network node, wherein the radio network node is configured to communicate over an air interface with a wireless terminal (also known as mobile station and/or user equipment (UE)). The method proposed in PCT/SE2013/050336 comprises scheduling pilots, including common pilots transmitted for channel estimation, for transmission over the air interface to the UE. The method further comprises making a determination whether additional pilots for data demodulation are also to be transmitted to the UE in addition to the common pilots transmitted for channel estimation. A corresponding method performed by the UE is also proposed. This method comprises making a determination regarding which pilots transmitted from the radio network node are to be utilized by the UE, the pilots transmitted from the radio network node including common pilots for channel estimation and additional pilots for data demodulation.
FIG. 1 illustrates an example signaling diagram used for signaling demodulation pilots. The radio network node (e.g., an evolved NodeB (eNB)) transmits common pilots continuously for Channel State Information (CSI) estimation (act 110). The UE may compute, estimate or otherwise determine CSI such as Channel Quality Information (CQI), Precoding Control Index (PCI), and Rank Information (RI) and report back (act 120) to the radio network node, e.g. over a High Speed-Dedicated Physical Control Channel (HS-DPCCH). Once the CSI report is received by the radio network node, the radio network node can determine whether only the common pilots are sufficient for data demodulation, or whether the additional pilots are also desirable. For example, this determination can be made based on parameters such as Signal to Noise Ratio (SNR), Signal to Interference plus Noise Ratio (SINR), block error rate (BLER), UE location, modulation and code rate, etcetera. The determination can e.g. be made by a pilot determination controller or a scheduler of the radio network node. If it is determined or otherwise concluded that additional pilots are needed or desirable, the radio network node can signal (i.e. transmit) information indicative of the need or desire to use additional pilots to the UE (act 130). For example, this information can be transmitted using a High Speed Shared Control Channel, HS-SCCH, order message. HS-SCCH order messages are known to persons skilled in the art and will therefore not be further detailed herein. If the UE is capable of decoding the HS-SCCH order message, the UE transmits an acknowledgement (ACK) message to the radio network node 100, e.g. over a HS-DPCCH (act 140). Subsequently, upon receipt of such ACK message, the radio network node transmits data to the UE 200 (act 150). The data includes the additional pilots. The data can e.g. be transmitted over a High Speed-Physical Data Shared Channel, HS-PDSCH. The UE then uses the additional pilots for demodulation until again informed by the radio network node. Act 160 is intended to reflect another, or new, order message over the HS-SCCH. Act 170 illustrates subsequent transmission of data over a downlink data channel, such as a High Speed-Physical Data Shared Channel (HS-PDSCH).